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Tahoe-LAFS Drop-Upload Frontend

  1. Introduction
  2. Configuration
  3. Known Issues and Limitations

Introduction

The drop-upload frontend allows an upload to a Tahoe-LAFS grid to be triggered automatically whenever a file is created or changed in a specific local directory. This is a preview of a feature that we expect to support across several platforms, but it currently works only on Linux.

The implementation was written as a prototype at the First International Tahoe-LAFS Summit in June 2011, and is not currently in as mature a state as the other frontends (web, CLI, SFTP and FTP). This means that you probably should not keep important data in the upload directory, and should not rely on all changes to files in the local directory to result in successful uploads. There might be (and have been) incompatible changes to how the feature is configured. There is even the possibility that it may be abandoned, for example if unsolveable reliability issues are found.

We are very interested in feedback on how well this feature works for you, and suggestions to improve its usability, functionality, and reliability.

Configuration

The drop-upload frontend runs as part of a gateway node. To set it up, you need to choose the local directory to monitor for file changes, and a mutable directory on the grid to which files will be uploaded.

These settings are configured in the [drop_upload] section of the gateway's tahoe.cfg file.

[drop_upload]

enabled = (boolean, optional)

If this is True, drop-upload will be enabled. The default value is False.

local.directory = (UTF-8 path)

This specifies the local directory to be monitored for new or changed files. If the path contains non-ASCII characters, it should be encoded in UTF-8 regardless of the system's filesystem encoding. Relative paths will be interpreted starting from the node's base directory.

In addition, the file private/drop_upload_dircap must contain a writecap pointing to an existing mutable directory to be used as the target of uploads. It will start with URI:DIR2:, and cannot include an alias or path.

After setting the above fields and starting or restarting the gateway, you can confirm that the feature is working by copying a file into the local directory. Then, use the WUI or CLI to check that it has appeared in the upload directory with the same filename. A large file may take some time to appear, since it is only linked into the directory after the upload has completed.

The 'Operational Statistics' page linked from the Welcome page shows counts of the number of files uploaded, the number of change events currently queued, and the number of failed uploads. The 'Recent Uploads and Downloads' page and the node log may be helpful to determine the cause of any failures.

Known Issues and Limitations

This frontend only works on Linux. There is an even-more-experimental implementation for Windows (#1431), and a ticket to add support for Mac OS X and BSD-based systems (#1432).

Subdirectories of the local directory are not monitored. If a subdirectory is created, it will be ignored. (#1433)

If files are created or changed in the local directory just after the gateway has started, it might not have connected to a sufficient number of servers when the upload is attempted, causing the upload to fail. (#1449)

Files that were created or changed in the local directory while the gateway was not running, will not be uploaded. (#1458)

The only way to determine whether uploads have failed is to look at the 'Operational Statistics' page linked from the Welcome page. This only shows a count of failures, not the names of files. Uploads are never retried.

The drop-upload frontend performs its uploads sequentially (i.e. it waits until each upload is finished before starting the next), even when there would be enough memory and bandwidth to efficiently perform them in parallel. A drop-upload can occur in parallel with an upload by a different frontend, though. (#1459)

If there are a large number of near-simultaneous file creation or change events (greater than the number specified in the file /proc/sys/fs/inotify/max_queued_events), it is possible that some events could be missed. This is fairly unlikely under normal circumstances, because the default value of max_queued_events in most Linux distributions is 16384, and events are removed from this queue immediately without waiting for the corresponding upload to complete. (#1430)

Some filesystems may not support the necessary change notifications. So, it is recommended for the local directory to be on a directly attached disk-based filesystem, not a network filesystem or one provided by a virtual machine.

Attempts to read the mutable directory at about the same time as an uploaded file is being linked into it, might fail, even if they are done through the same gateway. (#1105)

When a local file is changed and closed several times in quick succession, it may be uploaded more times than necessary to keep the remote copy up-to-date. (#1440)

Files deleted from the local directory will not be unlinked from the upload directory. (#1710)

The private/drop_upload_dircap file cannot use an alias or path to specify the upload directory. (#1711)

Files are always uploaded as immutable. If there is an existing mutable file of the same name in the upload directory, it will be unlinked and replaced with an immutable file. (#1712)

If a file in the upload directory is changed (actually relinked to a new file), then the old file is still present on the grid, and any other caps to it will remain valid. See docs/garbage-collection.rst for how to reclaim the space used by files that are no longer needed.

Unicode names are supported, but the local name of a file must be encoded correctly in order for it to be uploaded. The expected encoding is that printed by python -c "import sys; print sys.getfilesystemencoding()".

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